In conventional pneumatic tires, stones are sometimes held or trapped within grooves that are formed on the tread area of a pneumatic tire fitted to a vehicle, during its travel. Furthermore, such stones may penetrate the bottoms of the grooves due to rolling of the pneumatic tire, and so-called “stone drilling” may occur. If the stone drilling occurs in the above manner, then the stones having penetrated causes cracking of the groove bottoms and damage to a belt layer when the stone penetration occurs so deeply. If the belt layer is damaged, water comes into the belt layer from the outside through a hole made by the stone drilling, and steel forming the belt layer is rusted, which may lead to tread separation.
Some of the conventional pneumatic tires have protrusions in the grooves in order to minimize stone trapping in the grooves. For example, in Patent Literature 1, a pneumatic tire has circumferential grooves, along which protrusions are provided. These protrusions can minimize stone trapping in the circumferential grooves. Furthermore, in the Patent Literature 1, a protrusion is located at an intersection between a circumferential groove and a lateral groove, and is formed so as to fit also along the lateral groove. Stones or the like are easily held in the portion where the grooves intersect each other, and stone trapping thereby easily occurs therein. However, by forming the protrusion disposed at this portion into such a form that the protrusion fits also along the lateral groove, the stone trapping hardly occurs. Since the pneumatic tire runs on the snowy road, snow traction performance is also required. High snow traction performance can be obtained by increasing the capacity of the grooves to cause the snow on the road to enter the grooves, and by pushing aside the snow. Therefore, the protrusions, which are almost cuboids, are arranged at intervals to ensure the capacity of the grooves.
[Patent Literature 1] Japanese Patent Application Laid-Open No. H03-67706.